1. Field of the Invention
The present invention relates to a vibration damping device used for example as an automobile engine mount, a suspension member mount or the like.
2. Description of the Related Art
From the past, vibration damping devices have been known as one type of vibration damping connecting body or vibration damping support body that is interposed between members constituting a vibration transmission system and does vibration damping connection of these members to each other. As a vibration damping device, for example, as shown in Japanese Unexamined Patent Publication No. JP-A-11-257397, used is a constitution with which the vibration damping device main unit for which a main rubber elastic body is fixed to the outer circumference surface of an inner shaft member is fit into a tube part of an outer bracket, and the tube part is fitted to the outer circumference surface of the main rubber elastic body non-adhesively.
Meanwhile, when the tube part is fitted non-adhesively to the outer circumference surface of the main rubber elastic body, it is necessary to restrict the relative displacement volume of the main rubber elastic body and the tube part. In particular, with the axial direction which is the fitting in direction of the main rubber elastic body, it is necessary to restrict the relative displacement volume of the vibration damping device main unit and the tube part so as to prevent falling out of the vibration damping device main unit from the tube part.
In light of that, the proposal with JP-A-11-257397 is that an overhang part is formed projecting further outward in the axial direction from both axial ends of the tube part. Then, after the tube part is attached to the outer circumference surface of the main rubber elastic body, the overhang part is bent to the inner circumference side of the tube part, and falling out of the main rubber elastic body is prevented by the abutment of the overhang part and the axial end surface of the main rubber elastic body.
However, with the vibration damping device equipped with this kind of retaining structure noted in JP-A-11-257397, after the main rubber elastic body is housed in the outer bracket tube part, it is necessary to provide an overhang part using press processing, welding or the like on the axial end part of the tube part, and there was the risk that the outer bracket structure would become complex, and that this would require time and labor for manufacturing. Also, when forming the tube part by bending a plate member equipped with the overhang part, if the plate member is too thin, there is the risk that the tube part rigidity will be insufficient, while on the other hand, if the plate member is too thick, there is the risk that it will be difficult to do the bending process of the overhang part. Furthermore, since it is necessary to bend the overhang part in a state with the main rubber elastic body housed in the tube part, the rigidity is reduced by partially forming the overhang part on the circumference or the like so that the bending process is easy, but with this kind of structure, there were also cases when depending on the size of the input load, the shape of the main rubber elastic body or the like, it was difficult to have sufficient load bearing to prevent falling out of the main rubber elastic body in the axial direction.
Japanese Unexamined Patent Publication No. JP-A-2009-293766 indicates a structure in which a protruding part projecting to the inner circumference side at the axial center of the outer bracket tube part is formed, and also, a concave groove open to the outer circumference surface of the axial center of the main rubber elastic body and extending in the circumference direction is formed. By doing insertion locking of the protruding part in the concave groove, the main rubber elastic body is prevented from falling out of the outer bracket. However, this kind of structure shown in JP-A-2009-293766 can be used as long as it is a main rubber elastic body having a leg part for which the shape does not greatly affect the vibration damping characteristics, but for example when a concave groove of a size for which sufficient retaining action can be obtained is formed on the main rubber elastic body such as that noted in JP-A-11-257397, there was the problem of an adverse effect on the vibration damping characteristics and durability due to the decrease in rubber volume. Meanwhile, when the concave groove is made smaller to suppress the effect on vibration damping characteristics and durability, the retaining action in the axial direction is insufficient, and there was the risk that the main rubber elastic body could fall out from the outer bracket during input of a large load.